Question

Heat transfer in vacuum occurs by:

• A. Conduction
• B. Convection
• C. Radiation
• D. Diffusion

Hint:

Remember:
- Conduction \(\rightarrow\) Solids (needs matter).
- Convection \(\rightarrow\) Fluids (needs moving matter).
- Radiation \(\rightarrow\) Vacuum or transparent media (does not need matter).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question asks to identify the mode of heat transfer that can take place through a vacuum (empty space without any material medium).

Step 2: Key Formula or Approach:
Heat transfer can occur via three primary modes:
1.

Conduction: Transfer of thermal energy through direct atomic/molecular contact.
2.

Convection: Heat transfer by the bulk movement of fluid molecules.
3.

Radiation: Heat transfer via electromagnetic waves (primarily infrared).

Step 3: Detailed Explanation:

• Need for a Material Medium:
- Both conduction and convection require a physical, material medium to facilitate heat transfer.
- Conduction relies on lattice vibrations (phonons) and free electron movement in solids.
- Convection relies on mass transport in fluids (liquids and gases).
- In a vacuum, there are no atoms or molecules present to carry out conduction or convection.

• Electromagnetic Radiation:
- Thermal radiation is governed by the Stefan-Boltzmann Law:
\[ E = \epsilon \sigma A T^4 \]
- It occurs via electromagnetic waves, which do not require any physical medium for propagation and can travel through a vacuum at the speed of light.
- A classic example is the transmission of solar energy from the Sun through the vacuum of space to the Earth.


Step 4: Final Answer:
Heat transfer in a vacuum occurs exclusively by thermal radiation.
Therefore, option (C) is the correct choice.